MySQL / Paging and search results

At the moment I'm adding a search option to one of my projects.
The search is working great, but sometimes giving too much results back to fit on one page.

I know how to do a paging on results from the MySQL (page 1, page 2 etc..), but how do you do this on a search result?

I see that the HowtoForge forum does this by using a "searchid=xxxxx".
Whats stored in the searchid? Is this the search terms that the user used for the search?
Also.. Is the searchid stored in a MySQL or in a session?